The present invention relates to part of a press section which serves to dewater a fiber web which is conveyed to and from an intermediate nip of the press section by a suitable felt or wire fabric. This intermediate press nip includes a pair of press rolls through which the above wire and fabric travel with the web adhering to the latter fabric while a second felt or wire fabric also travels through this intermediate press nip, lapping the other press roll so that at the intermediate press nip the web is compressed between the above fabrics. The press roll which engages the web-conveying fabric has a smooth surface while the other press roll is provided with a grooved surface or a surface having blind holes drilled therein, or an equivalent water-receiving recessed structure is provided. The plane which contains the axes of the above rolls is tilted with respect to the direction of travel of the web-conveying fabric in such a way that the latter fabric and the web conveyed thereby lap the smooth-surfaced press roll through a predetermined angle immediately subsequent to the intermediate press nip.
With certain press section constructions it is essential to remove water from the fiber web while this web remains continuously attached to a conveying belt or wire fabric. Such a construction is utilized, for example, when the strength of the fiber web is so small that it must necessarily be supported by a conveying wire or felt fabric while passing through the press nip. Also such a construction is desired in those cases where the fiber web has already at an earlier stage been shortened by being upset or creped in one way or another, while it is desired to avoid the tendency of the web to become elongated.
One of the practical solutions to this problem has been to provide at a press nip a suction press roll and a cooperating smooth-surfaced press roll which directly engages the fiber web. This web will of course tend to adhere to the smooth-surfaced roll, but it is maintained instead adhering to the conveying felt as a result of the suction at the suction roll. In this construction the water is removed from the web toward the suction roll through the web-conveying felt.
Another possible solution is to provide at a suction press nip of the above type an additional felt which travels between the suction roll and the web-conveying felt. With such a construction the water will then escape from the web directly through this additional felt toward the suction roll.
It is also possible to utilize double-felted press nips without a suction roll. In such constructions adhering of the web has been achieved by suitable selection of the felts in that the web-conveying felt is selected to have a smooth surface and to be more compact, or in other words of a denser construction, than the other felt. As a result the web-conveying fabric remains comparatively wet subsequent to the press nip. Various felt qualities also have an effect on the surface characteristics of the paper, giving rise to differences in smoothness or roughness. In any case, such a solution requires greater attention with respect to maintaining web adherence than would be desirable in view of other operational and quality factors.
The adherence of the web is of course assured to a greater degree if the web forming itself has taken place against the web-conveying felt. With such an arrangement the felt itself operates as part of the web-former, for example in cooperation with a wire fabric at the opposite side of the web. A construction of this type, and the further treatment of the felt-web combination thus obtained in the press section, must be viewed as a special solution which is not considered here.